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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id b17sm954051edy.47.2021.10.20.03.45.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Oct 2021 03:45:15 -0700 (PDT) Message-ID: <18aed000-47f7-1fb7-d898-55a94bb1ec74@redhat.com> Date: Wed, 20 Oct 2021 12:45:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [PATCH v5] KVM: emulate: Don't inject #GP when emulating RDMPC if CR0.PE=0 Content-Language: en-US To: Wanpeng Li , linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel References: <1634724836-73721-1-git-send-email-wanpengli@tencent.com> From: Paolo Bonzini In-Reply-To: <1634724836-73721-1-git-send-email-wanpengli@tencent.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/10/21 12:13, Wanpeng Li wrote: > From: Wanpeng Li > > SDM mentioned that, RDPMC: > > IF (((CR4.PCE = 1) or (CPL = 0) or (CR0.PE = 0)) and (ECX indicates a supported counter)) > THEN > EAX := counter[31:0]; > EDX := ZeroExtend(counter[MSCB:32]); > ELSE (* ECX is not valid or CR4.PCE is 0 and CPL is 1, 2, or 3 and CR0.PE is 1 *) > #GP(0); > FI; > > Let's add a comment why CR0.PE isn't tested since it's impossible for CPL to be >0 if > CR0.PE=0. > > Reviewed-by: Sean Christopherson > Signed-off-by: Wanpeng Li > --- > v4 -> v5: > * just comments > v3 -> v4: > * add comments instead of pseudocode > v2 -> v3: > * add the missing 'S' > v1 -> v2: > * update patch description > > arch/x86/kvm/emulate.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index 9a144ca8e146..c289809beea3 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -4222,6 +4222,9 @@ static int check_rdpmc(struct x86_emulate_ctxt *ctxt) > if (enable_vmware_backdoor && is_vmware_backdoor_pmc(rcx)) > return X86EMUL_CONTINUE; > > + /* > + * It's impossible for CPL to be >0 if CR0.PE=0. > + */ > if ((!(cr4 & X86_CR4_PCE) && ctxt->ops->cpl(ctxt)) || > ctxt->ops->check_pmc(ctxt, rcx)) > return emulate_gp(ctxt, 0); > Queued, thanks (with a slightly more verbose comment). Paolo